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cache: manage negative entry list with a dedicated lock

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Since negative entries are managed with a LRU list, a hit requires a
modificaton.

Currently the code tries to upgrade the global lock if needed and is
forced to retry the lookup if it fails.

Provide a dedicated lock for use when the cache is only shared-locked.

Reviewed by:	kib
MFC after:	1 week
This commit is contained in:
mjg 2016-09-04 08:58:35 +00:00
parent 42f18d4efb
commit 1304091d66
1 changed files with 19 additions and 6 deletions
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25
sys/kern/vfs_cache.c
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@ -186,6 +186,9 @@ RW_SYSINIT(vfscache, &cache_lock, "Name Cache");
#define CACHE_WLOCK() rw_wlock(&cache_lock)
#define CACHE_WUNLOCK() rw_wunlock(&cache_lock)
static struct mtx_padalign ncneg_mtx;
MTX_SYSINIT(vfscache_neg, &ncneg_mtx, "Name Cache neg", MTX_DEF);
/*
* UMA zones for the VFS cache.
*
@ -436,12 +439,21 @@ SYSCTL_PROC(_debug_hashstat, OID_AUTO, nchash, CTLTYPE_INT|CTLFLAG_RD|
* Negative entries management
*/
static void
cache_negative_hit(struct namecache *ncp)
cache_negative_hit(struct namecache *ncp, int wlocked)
{
rw_assert(&cache_lock, RA_WLOCKED);
if (!wlocked) {
rw_assert(&cache_lock, RA_RLOCKED);
mtx_lock(&ncneg_mtx);
} else {
rw_assert(&cache_lock, RA_WLOCKED);
}
TAILQ_REMOVE(&ncneg, ncp, nc_dst);
TAILQ_INSERT_TAIL(&ncneg, ncp, nc_dst);
if (!wlocked)
mtx_unlock(&ncneg_mtx);
}
static void
@ -680,16 +692,17 @@ negative_success:
return (0);
}
if (!wlocked && !CACHE_UPGRADE_LOCK())
goto wlock;
counter_u64_add(numneghits, 1);
cache_negative_hit(ncp);
cache_negative_hit(ncp, wlocked);
if (ncp->nc_flag & NCF_WHITE)
cnp->cn_flags |= ISWHITEOUT;
SDT_PROBE2(vfs, namecache, lookup, hit__negative, dvp,
nc_get_name(ncp));
cache_out_ts(ncp, tsp, ticksp);
CACHE_WUNLOCK();
if (wlocked)
CACHE_WUNLOCK();
else
CACHE_RUNLOCK();
return (ENOENT);
wlock: